Eclipse tabs repositionning

Juno by default doesn't present the MRU (Most Recently Used) tab behaviour that you see in Indigo (it never worked quite right) and instead uses the Editor document order.

I believe you can re-activate it be either switching to the Classic theme in Preferences>General>Appearance or by editing the CSS. See http://wiki.eclipse.org/Eclipse4/CSS

.MPartStack {
    swt-mru-visible: true;
}

Don't forget to restart Eclipse to make it use the new parameters.

Apparently this option was added in Eclipse Mars 4.5:

Window -> Preferences -> General -> Appearance ->

Visible tabs on overflow:

[X] Show most recently used tabs